Something very relevant from another Lynne (the linguist Lynne Murphy � she was discussing BrEng. anticlockwise v AmEng. counterclockwise):

"In BrE the second syllable of anti-clockwise is pronounced like tea. Americans often (but not always) pronounce anti- with a second syllable like tie, which can help in distinguishing it from ante-. Some discussion of the variation in AmE pronunciation of anti- can be found here. For me, it �s partly on a word-by-word basis: �tea � in anticlimax, but �tie � in anti-Communist. I think if I form a new word with it (say, if I �m anti-pigeon), I �d pretty regularly use �tie �. But that �s what I think. And we �re all pretty bad rememberers of what we do say and we �re often bad judges of what we would say. So, unless someone records me unawares saying antipigeon, we may never know..."

You can find the full post here.